1. Field of the Invention
This invention relates, in general, to resin bonded glass fiber columns suitable for use as utility poles, light standards or the like and their method of fabrication, and in particular, to poles of unique cross sectional shape and the method of forming these poles on a removable finned mandrel to produce an exceptionally light but strong pole.
2. Description of the Prior Art
At present, most lighting standards and utility poles are constructed of wood and thus have the inherent drawbacks associated with wood such as relatively rapid deterioration from exposure to the elements and great weight which make the poles difficult to install and replace. Wooden core poles sheathed with fiberglass and thus having substantially increased useful life are known, such as shown for example in U.S. Pat. No. 3,562,403, as are hollow fiberglass poles formed on a non-removable mandrel such as a cardboard tube as shown in U.S. Pat. No. 2,870,793. Further, the broad concept of continuously wrapping resin coated glass fibers about a mandrel, allowing the resin to at least partially cure and then removing the mandrel to form continuous piping or tubing is also known as shown by U.S. Pat. Nos. 3,407,101 and 3,522,122, as is the practice of making individual pieces of plastic pipe in a similar manner as shown for example in U.S. Pat. Nos. 2,614,058 and 3,470,917.
These patents disclose the production of relatively flexible tubular structures unsuitable for use as light standards or utility poles, and of relatively short structures which may be removed from their internal mandrels without the substantial difficulty encountered in the fabrication of long fiberglass poles in this manner. Most resins used to bond fiberglass shrink upon curing and thus it will be understood that a long fiberglass column allowed to cure on a cylindrical mandrel can present a very difficult removal problem. Releasing agents such as polyvinyl alcohol have been used to coat a mandrel prior to covering it with fiberglass as set forth in U.S. Pat. No. 3,429,758 but the effectiveness of these releasing agents has been found to be less than satisfactory where a chopped glass and resin mixture is sprayed on a mandrel of substantial length. Additionally in the past, it has not been possible to construct an all fiberglass pole of sufficient length to serve successfully as a light standard or utility pole which was strong enough to withstand the wind loading and the like expected to be encountered in common use without either employing a rigid central core of some type about which the fiberglass was laid, wrapped or sprayed or sandwiching a core material such as plastic foam between two layers of glass roving such as shown in U.S. Pat. No. 3,429,758.